This invention relates in general to seismic survey devices and, more specifically, to a system and method for power switching in seismic marine operations.
Marine seismic exploration is an important tool for locating off-shore reserves. Typical explorations are performed by placing many sensors (e.g., hydrophones and/or geophones) on the ocean floor or on a towed streamer. These sensors receive seismic data which is then digitized by electronic modules distributed on the cable and sent to a recording system. The power for these electronic modules is supplied by the recording system and sent down the cable to the modules. A typical marine acquisition system may consist of approximately 1000 sensors spaced along the cable. The total length of a cable with this many sensors can be on the order of tens of miles. This cable is divided into multiple sections which are hooked up between electronic modules. A typical cable section may be 500 to 2500 feet in length.
The cable sections, sensors, and electronic modules are prepared above water and then deployed in the water. The deployment process can take several hours. Once deployed, it is often difficult to keep the cable sections from being damaged. This is due, in part, to the fact that marine explorations are typically deployed in areas populated with numerous obstacles, such as drilling and production platforms and debris therefrom. Also, sharp rocks, marine life, and even the deployment equipment itself can cause cable damage. This cable damage often causes electrical leakage currents to flow into the water. Electrical leakage currents can degrade seismic data quality, and also cause safety problems. For this and other reasons, a damaged cable section that has electrical leakage will generally have to be replaced before exploration can continue.
To replace a damaged cable, the entire system is returned to the surface; the damaged cable section is repaired or replaced; and the entire system is deployed again. Such action is extremely detrimental to the exploration in terms of time, resources, and cost. For example, replacing a single cable section requires several hours of down time. Also, the action requires the use of one or more ships to raise and re-lower the cable. Furthermore, after being repaired or replaced, the cable and accompanying sensors are typically not returned to their exact previous location, and therefore the seismic data becomes corrupted.
Therefore what is needed is a method and apparatus for making the marine exploration system more tolerant to cable damage thus allowing it to remain operational for longer periods of time.